Circulating GH levels are increased, and IGF-I levels decreased, in type I diabetes mellitus. The elevated GH levels may aid development of diabetic microvascular complications. This study aims to determine (1) whether the suppression of GH secretion by IGF-I infusion, previously demonstrated in normal young adults, also occurs in type I diabetes, and (2) the time of onset, and time to recovery from this suppression if it occurs, and to relate this to changes in plasma total and free IGF-I levels.